Aromatic polycarbonates are well known, commercially available materials having a wide variety of applications in the plastics art. These polymers may be prepared by reacting a dihydric phenol, for example, 2,2-bis(4-hydroxyphenyl)propane, with a carbonate precursor, for example, phosgene, in the presence of an acid binding agent. In general, aromatic polycarbonates exhibit good resistance to attack by mineral acids, are readily moldable, and are physiologically inert.
Included among the known aromatic polycarbonates are tetraalkyl-substituted homopolycarbonates and copolycarbonates, as described in Serini et al., U.S. Pat. No. 4,172,103. As disclosed by Serini et al., the tetraalkyl-substituted polycarbonates are useful in compositions with homopolymers and copolymers of olefinically unsaturated monomers, such as polystyrene.
In generally, blends of aromatic polycarbonates and polystyrene are normally flammable. They are known to be rendered flame retardant, however, by the incorporation of bromine into the polycarbonate structure, for example, by the use of polycarbonate copolymers of tetrabromo bisphenol-A and tetramethyl bisphenol-A as disclosed in U.S. Pat. No. 3,890,266, or by the inclusion of conventional low molecular weight flame retardant additives such as decabromodiphenyl ether.